1. Field of the Invention
The present invention relates to a vibratory roller and more specifically to a vibratory roller of the type that is adapted for use to compact base material in narrow spaces such as at the bottom of trenches.
2. Description of the Related Art
Many different types of vibratory rollers have been designed for use in compacting base and subbase materials in trenches, foundations, utility excavations, roads and the like. Applicant is aware of the following prior patents showing vibratory rollers: U.S. Pat. No. 3,153,993, J. E. Keppler, issued Oct. 27, 1964; U.S. Pat. No. 3,395,626, G. D. Garis et al, Aug. 6, 1968; U.S. Pat. No. 3,605,583, J. E. Keppler, Sept. 20, 1971; U.S. Pat. No. 3,778,177, E. J. Haker, Dec. 11, 1973; U.S. Pat. No. 3,814,531, J. T. Carnahan et al, June 4, 1974; U.S. Pat. No. 4,187,034, E. J. Haker et al, Feb. 5, 1980; and DE 39 20 316 Al Offenlegungsschrift, Dec. 28, 1989.
All of the above cited prior patents disclose vibratory rollers that include some type of frame structure which may compose a single frame or interconnected front and rear subframes; rollers, or a combination of rollers and support wheels; a suspension means for mounting the roller on the frame structure; a steering means; a prime mover of some type which may include a hydraulic drive for driving the wheels or rollers to move the vibratory roller over the ground; and an exciter means for generating a vibration force. The exciter means includes heavy eccentric weights that are rotated to produce vertical forces which are transmitted to the rollers to compact the base material under the roller during operation. The exciter means is mounted on the upper portion of the frame, or concentrically on the axle of the roller either externally or internally of the roller.
There exists a long-standing practice by contractors to dig trenches having as narrow a width as possible to reduce the amount of material excavated and subsequently backfilled thus lowering costs. Trenches narrower than 24 inches are common. Various types of utilities are frequently installed in such trenches and settling of the base material in the bottom of the trench can result in damage or destruction of whatever type of installation has been placed in the trench. If fluid carrying pipes are installed, settlement could cause breakage and result in pollution of soil and ground water. Therefore, laws and regulations have become increasingly strict in requiring that the base material in the bottom of the trench be compacted. In narrow trenches such compacting is usually done with small hand operated compactors and this is very time-consuming and dangerous to the operator. Remote controlled, self-propelled vibratory rollers are known but those designed to be narrow enough in width to be lowered into narrow trenches, even those less than 24 inches wide, have not been entirely satisfactory.
In the prior art, design requirements for vibratory rollers are well defined. It has long been known that one requirement for a vibratory roller is that it should have lateral stability to minimize the risk of tipping. To meet this requirement the vibratory rollers are normally made quite wide and lateral stability is thus assured. When the vibratory roller is to be usable in a trench, a known second requirement must be met. The second requirement is that the vibratory roller must compact all of the base material in the trench including areas up to the side wall of the trench. To meet this requirement, the vibratory roller is designed so that no components will extend laterally beyond the width of the roller drum which is in compacting contact with the base material. To eliminate lateral projections, all components are arranged vertically on top of the roller drums and the lateral stability requirement, as mentioned above, is met by making the roller drums as wide as possible. As trenches have become narrower, the lateral stability requirement cannot be met by making the roller drum wider. The problem of how to lower the overall center of gravity of the vibratory roller to maximize lateral stability remains unsolved, and conventional heretofore-used designs do not offer any effective solutions to this problem of maximizing the lateral stability. Conventional vertical arrangements of components, and suspension systems for mounting the roller drums on the frame only tend to raise the overall center of gravity of a narrow vibratory roller.
Therefore, what is needed is a new and improved design and orientation of the vibratory roller components to maximize the effect of their weight in lowering the overall center of gravity of the vibratory roller to enhance lateral stability. In addition, an improved suspension system is needed to maximize the concentration of the load forces of all of the components in a manner that will operate to further contribute to the lateral stability of a narrow vibratory roller.